The present invention relates to an inertia drive type starter motor for an internal combustion engine.
Inertia drive type starter motors rely on inertia of the pinion or clutch mechanism to move the pinion from a rest position to an engaged position against a spring force when the motor is switched on. Such motor drives have been used successfully but do suffer from false starts whereby the pinion is disengaged prematurely by sudden rotation of the engine being started which occurs not only when the motor starts but also when the engine misfires or fires but does not start. These false starts disengage the starter motor pinion requiring the starting sequence to be re-initiated. They can also suffer from bounce out or pump out which is a condition where the pinion oscillates along the shaft while engaging the engine ring gear and is a condition that can result in complete disengagement.
Thus a positive engagement mechanism for an inertia drive is desirable. Two such type drives are shown in U.S. Pat. No. 2,923,162 and U.S. Pat. No. 4,502,429. U.S. Pat. No. 4,502,429 shows a device which is very complex while U.S. Pat. No. 2,923,162 shows a device wherein the inertia drive is not assisted by the holding mechanism.
According to one aspect thereof, the present invention provides an electric starter for an internal combustion engine comprising: an electric motor having a housing and a rotatable armature shaft extending therethrough, the shaft having a helical spline portion; a pinion gear mounted for selectively engaging a ring gear of the engine; a clutch assembly for transmitting torque between the shaft and the pinion gear, the clutch assembly having a driving part and a driven part, the driving part having an internal helical spline portion engaging the helical spline portion of the shaft whereby relative rotary movement between the shaft and the driving part creates axial movement of the clutch assembly along the shaft, and the pinion gear being fixed for rotation with the driven part; and a solenoid for holding the pinion gear in engagement with the ring gear wherein the solenoid has a toroidal coil and a tubular plunger located about the shaft between the motor housing and clutch assembly, the tubular plunger having a radially extending flange at a first end which is arranged to be attracted to the radial housing wall toward the coil.
According to a second aspect, the present invention provides a solenoid comprising a housing; a cap fitted to the housing and defining an internal void, the housing and the cap each having a through hole defining therebetween a through passage having an axis; a toroidal coil fitted to the housing about the through passage; a bearing fitted to the through hole in the housing and having a through hole aligned coaxially with the through passage; and a plunger having a tubular body extending axially along the through passage and slidably retained in the through hole of the bearing, the plunger having a radially extending flange at a first end of the tubular body.